The present invention relates to magnetic storage apparatus and more particularly to track seeking and following operations usable for accessing a given record track in such apparatus.
Magnetic recording devices have been employed for many years for use in conjunction with data processing apparatus. It is a desire in employing such apparatus to reduce access time for making a greater efficient use of the associated data processing apparatus. Such desires are most often manifested by increased recording data densities, both by increasing lineal density along the record track length, as well as increasing the track density. In many of the devices, particularly of the DASD or rotating magnetic disk type, one or more transducers are mounted on a radially movable carriage such that any track can be accessed by the supported transducer. Such an arrangement requires servo-positioning functions to ensure that the transducer faithfully scans a record area defined as a record track. At relatively low track densities, relatively simple apparatus may be employed; however, as track densities increase, the problem becomes asymptomatically acute. It is to the latter type of storage apparatus that the present invention is most advantageously used.
The above-referenced Sippel patent discloses that interleaving servo-positioning patterns for track following with data signals provides certain advantages. However, to precisely and rapidly radially locate a given track presents severe servomechanism problems. To this end, the cited copending patent applications teach that by grouping a given number of tracks into so-called "bands", access time can be reduced; that is, an initial accessing motion locates the transducer within a band of tracks. Subsequent to such "coarse" positioning movement, the servomechanism then senses signal patterns recorded on the disk, or other member, for locating a track within the band of tracks and for ensuring that the transducer faithfully follows the defined record track area.
Another important factor in constructing such magnetic memory apparatus is the cost factor. Accordingly, it is highly desirable to make operation low cost by using simple circuits and, at the same time, provide a greater degree of reliability such that actual access time to a record in the magnetic recorder is minimized.